1. Field of the Invention
The present invention relates to heat exchangers which are adapted to transfer heat energy between a fluid flowing through a tube and a gas in contact with the plate fins of the coil. More particularly, the present invention applies to heat exchanger coils particularly known as plate fin coils for use in the air conditioning and refrigeration industry. Typically these coils have refrigerant flowing through a circuit formed by tubular members and air flowing over the plate fins connected to the tubular members.
2. Description of the Prior Art
Formed coils are often used in the refrigeration and air conditioning industry when a heat exchanger coil is desired that will fit within a small container and yet must be of sufficient size that a single pass within the container will be insufficient to meet the load requirements of the unit. Many heat pump applications involve the use of an outdoor coil wherein the coil is either circular, L-shaped or U-shaped and wherein multiple row coils are necessary. This multiple row coil is usually arranged such that the first row of the coil is adjacent to the source of gaseous material to which or from which heat is to be transferred and the other rows of the coil are located interior thereof. Consequently, to fit this multiple row coil within the particular enclosure it is necessary that the radius of curvature of the bends in the interior coil be less than that of the exterior coil. Consequently, if two coils of the same length are bent on a different radius of curvature the ends of the coils will not be flush, resulting in uneven heat transfer characteristics. To overcome this problem, formed coils have been built of varying coil row lengths. Using a two roll coil for example the exterior coil is designed to have a greater length than the interior coil consequently, both coils will extend between the same locations and the desired heat transfer characteristics for the unit will be achieved.
The construction of previous formed heat exchangers involved forming a stack of fins for each coil row, lacing the fins with the appropriate length tubing, installing a tube sheet which fits the ends of the coil rows, inserting return bends to complete the fluid flow circuit through the tubes and thereafter assembling and bending both coils. The shorter coil is bent about a smaller radius of curvature than the longer coil so that the previously uneven coil ends are even after bending. This process involves the actual assembly of two or more separate coils and subsequent joining.
The present invention by the use of sheets of fins connected by rupturable tabular portions allows simultaneous lacing of the longer hairpins of the exterior coil and the shorter hairpins of the interior coil. The longer hairpins after the lacing operation obviously extend further from the fin pack than the shorter hairpins. The common tube sheet at the end of the fin pack furthest from the curvilinear part of the hairpins has been mounted prior to the lacing such that when the lacing operation occurs the hairpins are also inserted through the tube sheet. The coil rows are then expanded such that the diameter of the hairpins are increased to form a tight fit with the fins. During this expansion the tabular portions connecting the fins within the sheets are ruptured such that the fins of a sheet may be displaced in relation to each other to be evenly spaced along the respective hairpins. Mechanical expansion with "bullets" (expansion elements) further serves to space the fins along the hairpins as a result of the travel direction of the "bullets" downward thru the hairpins. The displacement results in the fins being separately spaced along the length of each hairpin. The coil rows are then bent to the desired configuration such that the hairpins curvilinear part ends in the desired location. A method has been provided for the assembly of formed coils which allows the short and long hairpins to be simultaneously laced and thereafter for even distribution of the fins within both the short and long coil rows without the necessity of individually assembling and forming each row.